1. Field of the Invention
The present invention relates to spacecraft rocket propulsion systems and, more particularly, to the utilization of fluid bipropellant by spacecraft rocket propulsion systems.
2. Description of the Related Art
A recurrent objective in the implementation of spacecraft rocket propulsion systems powered by a fluid bipropellant is the efficient utilization of the bipropellant. Surplus bipropellant which remains after a rocket engine has boosted a spacecraft to a desired trajectory above the earth represents excess mass carried aloft with the spacecraft. This excess mass can add to the cost of launching a spacecraft and can degrade spacecraft performance by, for example, adding to the total spacecraft mass which must be moved during station keeping maneuvers when a spacecraft is in geostationary orbit.
Unfortunately, the relative rates at which the respective constituents of a bipropellant are consumed is not easily predictable. Thus, enough of each bipropellant constituent typically is provided so that the spacecraft will not run short of one or the other bipropellant constituent before reaching the desired trajectory even if one constituent is consumed more rapidly than origianlly predicted. When the spacecraft does not consume the extra bipropellant, however, a surplus results.
In the past, various techniques have been employed in order to more efficiently utilize the bipropellant in order to avoid such surpluses. For example, during the firing of a rocket engine, the rate of consumption of each bipropellant constituent has been measured, and its flow rate to the rocket engine has been adjusted accordingly in order to achieve more complete consumption of both bipropellant constituents. Furthermore, in the case of some spacecraft of the type which have had large numbers of launchings, sufficient data on their rocket engine in-flight performance has been compiled to provide a relatively accurate estimate of how much of each bipropellant constituent is needed for a given mission.
While earlier techniques for efficiently utilizing fluid bipropellant generally have been successful, there have been shortcomings with their use. For example, the measurement and adjustment of a bipropellant constituent's flow rate during the firing of a rocket engine often cannot be performed with sufficient accuracy. Furthermore, when a type of spacecraft has not had the benefit of numerous launchings in which to compile bipropellant consumption rate statistics, there may be insufficient data to accurately predict the rates of consumption of the bipropellant constituents during a particular mission.
Thus, there has been a need for a method for more efficiently controlling the utilization of fluid bipropellant by a spacecraft. The present invention meets this need.